When you want to use a second monitor it's of course the best to use a monitor port located on your computer. When that's not an option, then the USB32HDEH from Startech.com is a practical solution, especially since you don't even have to sacrifice one of your USB 3.0 ports.
Slow computer got you down? Maybe a hardware upgrade should be in your cards, if so this guide to the Fundamentals of Upgrading a PC is an invaluable read. PCSTATS Tips